Right now we have XCMP lite that parachain send XCM to another parachain via relaychain route.
In future, we will have XCMP full that parachain send XCM to another parachain directly without any intermediary.

Currently, for many operations such as reserved transfer, the XCM is sent to relaychain, relaychain execute it, and dispatch a modified XCM to dest chain for execution. This is not XCMP compatible as there will be no intermediary chain to execute the XCM before delivering it to dest chain.

Relaychain should really only do the message delivery and no execution for HRMP. Otherwise XCMP-lite won't be XCMP-full compatible, which is the goal of XCMP-lite.